The present invention relates to production of blister bands in so-called blistering machines. More precisely, the present invention relates to a method and apparatus for forming the blister band of blister packs.
At present, blistering machines form blisters in a continuous band of heat-formable material and subsequently fill the obtained blisters with articles. Afterwards, the blister band, filled with articles, is closed by welding a sealing sheet and cut in portions to obtain single blister packs.
The band of heatxe2x80x94formable material is unwound from a bobbin and is conveyed on a horizontal plane between the opposite plates of a preheating station and then to the forming station, where suitable means form the blisters in the band, which is deformable due to the heat action. One of the disadvantages of known blistering machines derives from the scarce flatness of the obtained blister packs.
This is primarily due to the dilatation of the heat-formable band caused by the heating necessary to form the band, and to the subsequent shrinking of the band when it returns to the environment temperature, after the sealing sheet has been applied.
The shrinkage is not uniform due to the fact that the blister band is not physically homogeneous.
Another drawback of known machines derives from the fact that the shrinkage of the blister band is different from the shrinkage of the sealing sheet.
The latter drawback has been noted also in case the blister band has been made from a heat-forming material like polypropylene, preferred recently most of all for ecologic reasons.
It is to be noted that the shrinkage of the above mentioned material, and consequently, the bending of the blister band and subsequent blister packs continues for a long time after the forming and sealing steps, before the blister packs can reach a stabile state, which affects negatively also the subsequent production steps, e.g. piling and packaging the blister packs in boxes.
Although the bending of the blister packs does not compromise their fundamental function to contain and protect articles from external agents action, it constitutes a visible defect.
This defect is more visible if the blister packs are sold singularly instead of closed in a box.
A known technique for avoiding this problem includes partial heating of the heat-formable band, in practice only in the areas which are to be heat-formed, as described e.g. in the Japanese document No. 2.690.243.
According to the solution proposed by the above mentioned document, the heat-formable band is heated locally by a series of heating members, of gradually increasing dimensions, whose form is the same as the blisters to be formed.
The dimensions of the final heating members are almost the same as blisters dimensions.
This way, when the blisters are being formed, only the heated area, corresponding to the blisters area is deformed, and the surrounding area of the band remains not deformed.
The above mentioned technique resolves effectively the problem of substantially aesthetic nature, thus allowing to obtain essentially flat packs.
However, this solution causes a considerable reduction of the packages protection capacity, i.e. their primary function.
In fact, it is evident that the deformation of only one area of the band, whose dimensions are at most equal with the blister dimensions, cause a corresponding reduction of the band thickness in this area.
Therefore, the mechanical resistance of the band in the region of the blisters is reduced and likewise its capability of protecting the articles from external agents.
The object of the present invention is to solve the above problem, by proposing a method, which allows to form the blister band for making the blister packs maintaining its flatness and without changing its capability of protecting the articles packaged therein.
Another object of the present invention is to propose an apparatus for forming blister band, whose structure is simple, and which is functional and can be easily applied to known blistering machines.
The above mentioned objects are obtained, in accordance with the content of the claims, by a method for forming a blister band for blister packs in blistering machines, with a band of heat-formable material fed in an intermittent way with a step in a forward direction through a preheating station, a forming station for forming a regular series of blisters thus obtaining a blister band, a filling station for filling said blisters with articles, a sealing station for sealing the blister band with a sealing band, and a cutting station for cutting the blister band into single blister packs,. In said preheating station respective areas of said heat-formable band are heated gradually during a stepwise movement of said heat-formable band, the areas of the heat-formable band being distributed regularly within a cold grid-like zone and having extension suitably bigger than the extension of said blisters made in the region of said heated areas.
The method is carried out by an apparatus mounted on a machine including means for feeding the band of heat-formable material in an intermittent way by a step through a preheating station, a forming station for forming a regular series of blisters in the heat-formable band and obtaining a blister band, a filling station for filling the blisters with articles, a sealing station for applying, a sealing band to the blister band, and a cutting off station for cutting the blister band into single blister packs. The apparatus is characterized in that the preheating station includes heating means acting in a differentiated way to heat respective areas of said heat-formable band gradually during a stepwise movement of said heat-formable band, said areas of the heat-formable band being distributed regularly within a cold grid-like zone and having extension suitably bigger than the extension of said blisters made in the region of said heated areas.